1. Field of the Invention
The present invention relates to certain polymeric blends containing olefinic bisoleamides such as EBO (N,N-ethyleneBisOleamide) and ethylene copolymers such as ethylene vinyl acetate (EVA). The composition provides enhanced film forming properties in the production of monolayer or multilayer film products.
2. Description of Related Art
Ethylene vinyl acetate copolymers (EVA) are known and have a wide variety of applications in the industrial arts. EVA copolymers find commercial use in flexible, heat sealable, functional, and decorative hot-melt and solvent-applied coatings; as wax additives to impart toughness, flexibility, and adhesion; as blending resins to impart flexibility to brittle materials; and as a component of hot-melt and solvent-applied adhesives. It is also known that the vinyl acetate percentage in these copolymers can be varied and many such resins are sold under the trademark ELVAX(copyright) by E. I. du Pont de Nemours and Company. The present inventors have found that the film forming properties and processibility of this resin can vary with increasing vinyl acetate percentage and that high vinyl acetate copolymers (e.g. greater than about 0% VA by weight) can cause film processing problems. In an effort to solve this problem for high VA content ethylene copolymers, the inventors have surprisingly found that the addition of EBO improves film forming capability while minimizing negative effects on film properties such as clarity or other required physical parameters.
U.S. Pat. No. 4,510,281 describes the combination of EVA copolymers with certain oleamides to provide tack free pellets for industrial end uses. The oleamides and other esters described therein as additives improve the free-flowing properties of the pellets by incorporating into the polymer material prior to pelletization about 500-10,000 parts per million (ppm), especially 1000-5000 ppm, based on the polymer weight of an additive selected from the group consisting of N,Nxe2x80x2-ethylenebisoleamide, N,Nxe2x80x2-ethylenebiserucamide, N,Nxe2x80x2-diolelyladipamide, and N,Nxe2x80x2-dierucyladipamide. There is no specific teaching in this reference of the use of the compositions therein to produce a film or a film having processing advantages. There is, however, a general teaching relating to improvement of the handling and packaging throughput in actual production as a way to monitor good slip properties or antiblocking properties, especially for higher vinyl acetate content copolymers which could not be assessed by standard stick temperature tests. There is no requirement in the present invention that the additive be incorporated into the ethylene copolymer resin before pelletization.
Grades of ELVAX(copyright) containing, for example, N,N-ethylenebisoleamide have been sold by E. I. du Pont de Nemours and Company for industrial applications but have not been sold or used as packaging grade or film-forming resins. Grades of ELVAX(copyright) resins not containing an additive of this nature have been sold into the packaging market.
U.S. Pat. No. 4,956,232 discloses the use of slip additives in multilayer polypropylene films. Slip additives which may be used in making the films disclosed in the U.S. Pat. No. 4,956,232 patent are those which are incompatible with polypropylene, i.e., those which bloom to the surface from the core and skin layers. Non-ionic surfactants, such as the amides and carboxylic acids, were of particularly interest in this patent disclosure. Amides which were preferred included amides of carboxylic acids having at least five carbon atoms, for example, behenamide, linolenamide, arachidamide, ricinol-amide, palmitamide, myristamide, linoleamide, lauramide, capramide, perlargonamide, caprylamide, oleamide, steramide, N,Nxe2x80x2-ethylene bisoleamide, and the most preferred slip additive, erucamide. Carboxylic acids which were also described as useful included those having at least four carbon atoms, for example, butyric, caproic, caprylic, capric, lauric, lauroleic, myristic, myristoleic, pentadecanoic, palmitic, palmitoleic, margaric, stearic, oleic, linoleic, linolenic, ricinoleic, 2,3-dihydroxystearic, 12-hydroxystearic, behenic, eleostearic, arachidic, 2-ecosenoic, 4-eicosadienoic, 2-docosenoic, 2-tetracosenoic, 2,4,6-tetracosatrienoic and the like.
The slip additive in the above patent disclosure was preferably dry blended together with the polypropylene resin of layer (B) or the heat-sealable resin of layer (A) and then melt mixed. Alternatively, the additive could be incorporated into a minor portion of the resin as a master batch to form a high concentration mix of the additive and the resin. This could then be diluted to the appropriate proportion by the addition of more resin. There is no teaching herein of the use of any of these additives with an EVA resin or film.
U.S. Pat. No. 4,517,242 discloses a combination of ethylene copolymer resins and lubricating agents such as ethylenebisoleamides in glass coating compositions.
U.S. Pat. No. 3,879,330 discloses food wrap consisting of a vinylidene chloride polymer and a thermoplastic urethane polymer. The food wrap films of the invention can contain conventional additives such as lubricating additives, anti-blocking agents, anti-cling agents, and the like, all of which are known in the art. To illustrate, the food wrap films of the invention typically contain up to about 3 weight percent diatomaceous earth as an anti-blocking agent and up to about 2 weight percent of ethylenebisoleamide as a slip agent.
U.S. Pat. No. 5,468,444, describes the production of oriented thermoplastic films by blown-film extrusion. U.S. Pat. No. 5,453,209 discloses chemical metal and oil treating compositions and processes related thereto. U.S. Pat. No. 4,394,473 discloses polybutadiene bags and films. U.S. Pat. No. 3,645,822 discloses a method for providing multilayer films having improved slip properties. U.S. Pat. No. 5,468,444 discloses film-forming thermoplastic resins containing lubricants selected from aliphatic alcohol fatty acid esters obtained from an aliphatic alcohol having 1 to 12 carbon atoms, and preferably 1 to 6 carbon atoms, and a fatty acid having 10 to 22 carbon atoms, and preferably 12 to 18 carbon atoms, such as glycerol monooleate, glycerol di- or trioleate, glycerol triricinoleate, glycerol acetylricinoleate, methyl acetylricinoleate, ethyl acetylricinoleate, butyl acetylricinoleate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, polyoxyethylene glycerol, polyoxypropylene glycerol, sorbitan oleate, sorbitan laurate, polyethylene glycol sorbitan oleate, and polyethylene glycol sorbitan laurate; polyalkylene ether polyols, such as polyethylene glycol and polypropylene glycol; sugar fatty acid esters, epoxidized soybean oil, polyoxyethylene alkylamine fatty acid esters, polyoxyethylene alkylphenyl ethers; higher fatty acid amides having 12 to 22 carbon atoms, such as oleamide, stearamide, and erucamide; ethylene-bis-stearamide, ethylene-bisoleamide, polyethylene wax, polypropylene wax, and liquid paraffin. Suitable nucleating agents include inorganic substances, such as talc and silica. Suitable tackifiers include castor oil derivatives, low-molecular viscous polybutylene, sorbitan higher fatty acid esters, terpene resins, and petroleum resin.
The present invention relates to a polymeric film forming composition comprising an ethylene copolymer selected from an ethylene copolymer and an olefinic bisoleamide selected from an oleamide which affects film-forming properties of high ester content ethylene copolymer resins which heretofore have not produced film with the requisite physical properties. The present invention relates to a film-forming composition consisting essentially of an ethylene copolymer having a percentage of vinyl acetate monomer incorporated at 10% wt or higher relative to the ethylene, and an olefinic bisoleamide of the formula described herein wherein the oleamide additive is not required to be added to the composition prior to pelletization of the ethylene copolymer. The percentage of bisoleamide necessary to have the beneficial physical properties varies with the percentage of vinyl acetate in the film or extrusion coating and depends upon the thickness of the film or coating. Upon reading this disclosure, one of ordinary skill in the art can readily adjust the percentages accordingly.
The present invention also relates to a coating composition for extrusion coating comprising an ethylene copolymer having ethylene and an ester containing monomer (e.g. vinyl acetate or C1-C6 alkyl acrylate esters) and a bisoleamide of the formula described herein wherein the oleamide is not added to the composition prior to pelletization. The bisoleamide may be added post-pelletization and pre-extrusion.
The present invention also comprises a film having a first layer wherein the layer contains a polymeric composition comprising an ethylene copolymer selected from a copolymer of ethylene and a vinyl ester including vinyl acetate and an olefinic bisoleamide selected from a compound of the formula Rxe2x80x94C(O)xe2x80x94NHC2H4NHC(O)xe2x80x94R wherein R is selected from a C4-C25 saturated or unsaturated hydrocarbon. The invention also comprises a film having a first layer which contains a polymeric composition comprising an ethylene copolymer selected from a copolymer of ethylene and a vinyl ester including vinyl acetate and an olefinic bisoleamide selected from a compound of the formula Rxe2x80x94C(O)xe2x80x94NHC2H4NHC(O)xe2x80x94R wherein R is selected from a C4-C25 saturated or unsaturated hydrocarbon and a second layer comprising an ethylene acid ionomer selected from copolymers of ethylene and acrylic acid or methacrylic acid which are neutralized with a metal hydroxide or salt wherein the metal includes sodium, magnesium, calcium, etc. Such ionomers are sold under the trademark SURLYN(copyright) by E. I. du Pont de Nemours and Company. Any of the film or coating layers may also contain blends of, for example, polyethylene including linear low density polyethylene or ultra low density polyethylene. The relative percentages of the blends depends upon the operator""s target parameters and economic or other considerations.
The present invention further relates to a method of enhancing the slip characteristics of ethylene vinyl acetate films comprising adding an additive selected from an olefinic bisoleamide of the formula Rxe2x80x94C(O)xe2x80x94NHC2H4NHC(O)xe2x80x94R wherein R is selected from a C4-C25 saturated or unsaturated hydrocarbon to an ethylene vinyl acetate copolymer and producing the film. In particular, the bisoleamide permits effective slitting of blown film having a high percentage of vinyl acetate or other ester functionality wherein said film, absent the bisoleamide, would adhere or otherwise stick together to preclude or prevent effective slitting of the two-layer structure coming out of the blown-film pinch rollers. The invention also relates to a process for making a film comprising, (a) blending an olefinic bisoleamide selected from an olefinic bisoleamide of the formula Rxe2x80x94C(O)xe2x80x94NHC2H4NHC(O)xe2x80x94R wherein R is selected from a C4-C25 saturated or unsaturated hydrocarbon with an ethylene copolymer selected from copolymers having ethylene and an ester containing monomer including vinyl acetate to form a blend and (b) forming a film or extrusion coating from the blend having at least one layer.
The present invention improves the separation of film layers in blown film, both in the separation of the film xe2x80x9clayflatxe2x80x9d after the blown film stalk is pressed together or nipped which collapses the hollow film stalk upon itself or in subsequent separation of the layers of film on a film roll. In the former separation, the cylindrical hollow film stalk such as from a spiral blown film die, is flattened and collapsed between two moving nip rolls which flatten and press the cylindrical hollow film stalk into a two layer xe2x80x9clayflatxe2x80x9d sandwich. This film tube is cut at the edges and separated into two film layers, each of which are rolled onto a core forming rolls of film. The layflat is difficult to separate into the separate film layers, especially as the vinyl acetate monomer concentration increases in the ethylene copolymer resin that the film is made from. In the latter case of film layers on a roll, layers of film which have been wound onto a core or roll may be difficult to separate since the layers tend to stick together, again especially as the vinyl acetate monomer concentration increases in the ethylene copolymer resin that the film is made from. In both cases, the N,Nxe2x80x2-ethylenebisoleamide surface effects of reducing tackiness and improving film slip (increasing) properties occurs fast enough to allow separation of the film layers and therefore successful operation of these type processes.
The present invention also improves film cutting or slitting in film fabrication processes. The surface effects of the N,Nxe2x80x2-ethylenebisoleamide on the film occurs fast enough so that film cutting is often improved. Without the olefinic bisoleamide, the device which cuts the film such as a sharp razor, often catches on the film due to its tacky nature and poor slip qualities and results in the film jumping off the cutter or stretching of the film. Due to the quick action of reducing film tackiness and improving slip properties, in line film cutting is significantly improved with less drag forces between the cutting device and the film.
As summarized above, the present invention relates to ethylene copolymeric film-forming compositions containing an additive selected from an olefinic bisoleamide. The additive surprisingly provides enhanced film forming properties to an ethylene copolymer having a percentage of vinyl acetate monomer incorporated at 10 wt % or higher without impacting in a negative manner other film parameters such as clarity.
It has now been discovered that the film-forming and processing properties of polymers selected from the group consisting of
(a) copolymers of ethylene with an ester containing monomer such as vinyl acetate containing about 10-40 weight percent of vinyl acetate or ester containing monomer, or
(b) terpolymers of ethylene with vinyl acetate and carbon monoxide containing about 20-40 weight percent of vinyl acetate and 3-12 weight percent of carbon monoxide can be significantly improved by incorporating into the polymer material about 500-10,000 parts per million (ppm), especially 500-5000 ppm, based on the polymer weight of an additive selected from the group consisting of N,Nxe2x80x2-ethylenebisoleamide, N,Nxe2x80x2-ethylenebiserucamide, N,Nxe2x80x2-diolelyladipamide, and N,Nxe2x80x2-dierucyladipamide. For the purpose of this invention (the term xe2x80x9coleylxe2x80x9d means cis-9-octadecenyl, C8H17CHxe2x95x90CH(CH2)7CH2xe2x80x94; and the term xe2x80x9cerucylxe2x80x9d means cis-13-docosenyl, CH8H17CHxe2x95x90CH(CH2)11CH2xe2x80x94. This nomenclature is generally used in the trade, for example, for oleyl alcohol, oleylamine, and erucylamine.
Ethylene Copolymers
The ethylene copolymers of the present invention are selected from
(a) copolymers of ethylene with vinyl acetate containing about 10-40 weight percent of vinyl acetate, or
(b) terpolymers of ethylene with vinyl acetate and carbon monoxide containing about 20-40 weight percent of vinyl acetate and 3-12 weight percent of carbon monoxide. These copolymers are generally available under the trade names ELVAX(copyright) or ELVALOY(copyright) as sold by E. I. du Pont de Nemours and Company and are generally prepared from ethylene and various percentages of vinyl acetate and, if necessary, carbon monoxide; or
(c) copolymers of ethylene with ester containing monomers selected from methyl acrylate, butyl acrylate, isobutyl acrylate or terpolymers containing carbon monoxide.
The preferred ethylene copolymers are selected from ethylene vinyl acetate copolymers having a vinyl acetate percentage by weight relative to the ethylene in the range of 15-40 wt. % The most preferred ethylene vinyl acetate copolymer utilized in the film forming composition is selected from 15-33 wt. % or as exemplified herein.
For the purpose of this invention, the term xe2x80x9cvinyl acetate copolymerxe2x80x9d includes both the dipolymers and the terpolymers of ethylene with vinyl acetate and with carbon monoxide. Most commercial EVA dipolymers contain about 2-55% by weight of vinyl acetate. Terpolymers of ethylene with vinyl acetate and with carbon monoxide may contain about 18-40 weight percent of vinyl acetate and 2-12 weight percent of carbon monoxide. Dipolymers of ethylene with vinyl acetate are available, e.g., from E. I. du Pont de Nemours and Company, Wilmington, Del., under the. trademark Elvax(copyright); the terpolymers with carbon monoxide can be made according to the teachings of U.S. Pat. No. 2,495,286 to Brubaker and U.S. Pat. No. 3,780,140 to Hammer. As the vinyl acetate content of the copolymer increases, the copolymer tends to become increasingly sticky in both film and pellet states.
As discussed above, while use of the bisoleamides for antiblocking purposes is known, however, high VA content EVA copolymers are generally not used to produce film. The present inventors have discovered that the EVA copolymers with between 10-40% VA content can produce film with good properties provided that an olefinic bisoleamide is present in the composition as a primary additive.
Primary Additives
The olefinic bisoleamides are generally selected from a compound of the formula: Rxe2x80x94C(O)xe2x80x94NHCH2CH2NHC(O)xe2x80x94R wherein R is selected from C4-C25 saturated or unsaturated hydrocarbon moieties. In particular, the olefinic bisoleamides are selected from the group consisting of N,Nxe2x80x2-ethylenebisoleamide, N,Nxe2x80x2-ethylenebiserucamide, N,Nxe2x80x2-diolelyladipamide, and N,Nxe2x80x2-dierucyladipamide. The amides of this invention can be added to the copolymers by any convenient technique, for example, in the melt, as a dry powder below its melting temperature, or as a concentrate in the same or any compatible polymer. The additive is thoroughly blended with the polymer, which is then used to produce (via extrusion) the film or coating of the present invention.
The preferred olefinic bisoleamide is selected from N,N-ethyleneBisOleamide (EBO). N,Nxe2x80x2-Ethylenebisoleamide is available commercially from Carstab Corp. in Reading, Ohio, under the name xe2x80x9cAdvawaxxe2x80x9d 240; from Humko Sheffield Co., Memphis, Tenn., under the name xe2x80x9cKemamidexe2x80x9d W-20; and from Glyco Chemical Co., Greenwich, Conn. under the name xe2x80x9cGlycolubexe2x80x9d VL. The commercial product has a melting range of 113xc2x0-118xc2x0 C. It is recommended by its manufacturers as processing lubricant and antiblocking agent for various polymers and copolymers, especially as a slip agent for films. Its recommended level for these uses is 0.5-2%. As discussed above, however, there is no recommended use known for processing this additive with high VA content resins for film. The other additives can be made by known methods from readily available materials. Thus, N,Nxe2x80x2-ethylenebiserucamide is made by heating 1,2-ethylenediamine with erucic acid, and the remaining two amides are made by beating either adipic acid or its dimethyl ester with at least two equivalents of either oleylamine or erucylamine. The adipamide thus has the formula RNHxe2x80x94C(O)xe2x80x94(CH2)4xe2x80x94C(O)xe2x80x94NHR where R is either the oleyl or the erucyl group.
The relative weight percentage of olefinic bisoleamide to the ethylene copolymer ranges from 200-10,000 ppm. As indicated above, the percentage of bisoleamide will vary depending upon other parameters including VA content and thickness of the film or coating. In an 18 wt. % VA film, 1,000-3,000 ppm is the preferred range. In a 12 wt. % VA film, 700 ppm provides good slitting properties.
Additional Excipients
Additional excipients which are normally added to film forming or extrusion coating compositions include antiblock agents, fillers and other excipients known to those of ordinary skill in the art. As stated above, these additional ingredients can include other polymers, etc., including polyethylenes or ethylene copolymer ionomers such as those ionomers sold under the trademark SURLYN(copyright) by E. I. DuPont de Nemours and Company in additional or adjacent layers.
The film forming composition is prepared by mixing the olefinic bisoleamide with the ethylene copolymer as described below in a blown film forming process.
Film
Blown Film Forming Process
The vinyl acetate and ethylene copolymer resin, either containing the N,Nxe2x80x2-ethylene bis oleamide or mixed with pellets containing the N,Nxe2x80x2ethylene bis oleamide component, is conveyed to the feedthroat of an extruder. The extruder heats the resin particles, melts them and plasticates the copolymer into a blended melt and then pumps this melted copolymer material into a spiral die. The molten polymer is then pulled and formed into a circumferential hollow thin film stalk around an enclosed gas pocket or gas pressurized volume. The cooling of the molten polymer film which occurs just exit of the circular thin slit die opening and in drawing it over this enclosed gas volume provides sufficient strength to the polymer mass to pull and form or draw a hollow thin film stalk. This cylindrical thin film with the enclosed gas volume is at some point, collapsed between two counter rotating rolls pressing the cylindrical film together forming a two layer sandwich referred to as a layflat. The layflat is typically cut or slit on its edges forming 2 plies of film which are still layered together. The 2 film plies of the layflat are usually separated into individual films and rolled onto a turning core forming a roll of film. (This invention allows improved cutting and separation of the 2 film layer layflat for EVA films with VA levels of 1040%xe2x80x94due to its fast bloom and fast surface enhancing effects of reducing tackiness, sticking and COF (coefficient of friction).
Variants to this process include not slitting or separating the film layflat in the film forming process. If the circular die opening is horizontal (versus vertical in typical xe2x80x9cfilm blowingxe2x80x9d processing), the molten polymer forming into a film is sometimes referred to as profile or tubing extrusion.
Coating Operations
The vinyl acetate and ethylene copolymer resin, either containing the N,Nxe2x80x2ethylene bis oleamide or mixed with pellets containing the N,Nxe2x80x2ethylene bis oleamide component, is conveyed to the feedthroat of an extruder. The extruder heats the resin particles, melts them and plasticates the copolymer into a blended melt and then pumps this melted copolymer material into a coating die. The coating die distributes the molten polymer uniformly to a thin straight slit opening. Molten polymer flowing from the thin straight slit die forms a curtain or web which can coat a substrate moving beneath the slit opening. Just after the web contacts the moving substrate, the molten polymer is cooled by nipping, pressing or contacting the coating against a cool roll. The coated substrate is usually cut to a desired width and rolled onto a core. With higher VA EVA copolymer coating resins, the coating can stick to the cooling roll just after the molten polymer is dropped onto the moving substrate resulting in processing problems such as tearing the substrate and wrapping around the cooling roll. This invention facilitates using higher VA EVA copolymers due to the faster blooming effect of the slip and enhanced release properties that occur in the short time span prior to contacting the cooling roll.